The invention relates to a firing mechanism for a semiautomatic arm having a firing pin chamber disposed in elongation of a firing chamber, a firing pin being axially movable in said firing pin chamber between a neutral position in which its striking end is disposed in axial distance from a cartridge placed in the firing chamber, and a striking position in which the striking end is in contact with the percussion cap of the cartridge, means being provided to activate a trigger and thereby move the firing pin from the neutral position to the striking position.